1. Field of the Invention
The invention is generally directed to optical systems, such as spectrometers, and more specifically to methods and apparatus for extracting spectral information from a wavefront, such that select portions of the wavefront are sampled by a single optical device forming an Fizeau interferometer.
2. Description of the Related Art
To extract spectral information from electromagnetic radiation, such as infrared radiation, light, and ultraviolet radiation, spectrometers are often employed. One commonly used spectrographic technique to extract spectral information from collected light includes spectrally dispersing (i.e., physically spreading out) the light into its constituent wavelengths with a prism or diffraction grating. Once the constituent wavelengths of the light are spectrally dispersed, various wavelength detection techniques may be used to determine whether given wavelengths are present in the light. For example, the spectral dispersion of the light may by calibrated and a simple photocell used to detect a wavelength's presence within the spectral dispersion. Spectral dispersion of light has been used by scientists for centuries to determine the colors in light. For example, Sir Isaac Newton in the seventeenth century used prisms to demonstrate that light is comprised of many colors by using a first prism to spectrally disperse light and a second prism to recombine the light.
More recently developed techniques for extracting spectral information from light include Fourier transform spectroscopy techniques. Typical Fourier transform spectroscopy techniques include splitting a collected wavefront into two wavefronts and interfering the wavefronts to form an interference pattern. An optical path length of one of the two wavefronts is typically varied to collect intensity information from a number of interference patterns formed by the interfering wavefronts. The intensity information is then Fourier transformed to extract spectral information for the wavefront. Fourier transform spectrometers that include Michelson interferometers have been used with some success to extract spectral information from electromagnetic radiation, such as light. However, such Fourier transform spectrometers provide limited spectral resolution of collected wavefronts. Moreover, Michelson interferometers are inherently inefficient due in part to the beam splitters that are used to split wavefronts because the beam splitters reflect and absorb electromagnetic radiation that does not contribute to forming interference patterns. In low light spectroscopy measurements, for example, the loss of light in a Michelson interferometer tends to adversely affect the quality of extracted spectral information.
Accordingly, industry continues to strive to develop new Fourier transform spectrometers and techniques to extract spectral information from collected electromagnetic radiation. Specifically, Fourier transform spectrometers are desired that employ Fizeau interferometers.